The present invention relates to a method of transmitting data and more particularly relates to a method of transmitting data within pulse intervals of a rotational speed signal.
German patent application No. 196 50 935.1 discloses a method of this type wherein signal pulses are sent by a rotational speed sensor. The wheel rotational speed is determined from the time interval between signal pulses. Further data are transmitted in the pulse intervals. The data may represent, for example, the driving direction, the air pressure in the tire, the brake lining wear, or other quantities which are sensed on the wheel by sensors. The data are transmitted by binary signals. The signal levels of the signal pulses of the rotational speed sensor distinguish from the signal levels in data transmission in order to make possible a reliable distinction between a rotational speed signal which is relevant under driving safety aspects and the other data. The rotational speed signal must not be disturbed by the other data. The data transmission is triggered by a signal pulse of the rotational speed sensor in the object of the present invention. In this method, the number of the transmittable data is set by way of the duration of the transmission of one single information and the time available in a pulse interval. The maximum number of the transmittable data shall be set so that, with a duration of the pulse interval which corresponds to the maximum speed of the vehicle, the transmission of the data is completed before the next signal pulse of the rotational speed signal appears.
An object of the present invention is to improve the data transmission.
According to the present invention, this object is achieved by adapting the maximum number of the data transmittable in a pulse interval by setting as time, which corresponds to the length of the pulse interval, a value that results from at least one recently measured pulse interval in consideration of a maximum value of the wheel acceleration.
Thus, the number of the data transmittable in a pulse interval is adapted as a function of the driving speed. This renders it possible, for example, to transmit an increased number of data in the range of lower speeds of the vehicle. The configuration of the protocol in terms of the number of transmittable data is hence subject to minor limitations only.
In a preferred embodiment data are transmitted in a pulse interval which are relevant at high speeds.
In case that not all the data can be transmitted because the signal pulses of the rotational speed signal succeed each other too closely, the data which are relevant at high speeds are available nevertheless. Data which do not necessarily have to be transmitted at high speeds are, for example, the information about driving forward and backward because, initially, the driving speed must be reduced before the driving direction can be reversed. Possibly, the transmission of the information about the brake lining wear may also be omitted at high driving speeds. Normally, brake lining wear takes place only comparatively slowly so that a sufficient frequency of the transmission of this information is ensured with an occasional reduction of the driving speed, depending on the driving situation, or when filling-up or taking a break. On the other hand, the air pressure of the tire is considered to be an important information which should be transmitted also at high driving speeds.
The maximum number of the data transmitted in a pulse interval is adapted so that the data transmission is terminated as soon as the next signal pulse of the rotational speed signal appears.
It is favorable that there is no delay in time when the threshold of the signal level of the rotational speed signal is exceeded, in dependence on whether the signal level of the data transmission had the value xe2x80x980xe2x80x99 or xe2x80x981xe2x80x99.
In a preferred embodiment, a protocol of the data being transmitted is drafted, and an adaptation of the maximum number of data is effected by omitting individual or several data from the protocol, and wherein a minimum duration of at least one preceding pulse interval is determined with respect to any possible number of data being transmitted, in order to transmit this number of data. Further, it is determined by way of the established duration of at least one preceding pulse interval how many data may be transmitted as a maximum.
It shows that it can be found out comparatively easily and without great effort in real time how many data can be transmitted.
In a specific embodiment, the data transmission of a signal pulse of the rotational speed signal is discontinued when the duration of the data transmission is so long that already the next signal pulse of the rotational speed signal prevails. Favorably, it is taken into account in the evaluation of the rotational speed signal whether the information discontinued upon the appearance of the signal pulse of the rotational speed signal had the value xe2x80x980xe2x80x99 or xe2x80x981xe2x80x99.
It is an advantage that as many data as possible can still be transmitted. The transmission of the data is terminated only when this is actually necessary. The height of the signal level upon stopping the data processing indicates the time delay by which the corresponding threshold of the rotational speed signal is exceeded.
In a disclosed circuit arrangement, a signal of an oscillator and a second signal are sent to a counter in order to measure the at least one pulse interval. The second signal represents the appearance of a signal pulse of the rotational speed signal.
This permits easily determining the duration of the pulse interval, on the one hand. On the other hand, it is easy to determine by way of this pulse interval and the table how many data can reliably be transmitted.